This invention relates to a gaging device, and particularly to one of the caliper type, adapted for measuring dimensions of work pieces by the difference in position between two probe tips.
Gaging devices are in widespread use in industrial applications. It is frequently necessary during machining or other fabricating processes to make precise dimensional measurements of features of a work piece. For example, during an internal grinding operation, it is often necessary to measure the inside diameter of a workpiece to stop the grind cycle when correct size has been achieved. Numerous types of gaging devices are presently in use. Typically, these devices include two or more probe tips, which are capable of relative movement upon contacting the features to be measured. The probe tips are coupled to a measuring device to provide an output related to the difference in position of the probe tips. For example, so-called air gage devices can be used in which a moveable, variable obstruction device causes a change in pressure drop across an orifice to occur with changes in relative probe tip positioning. An external air source and pressure measuring system is used to provide an output related to the dimension being gaged. Other devices, such as linear variable differential transformers (LVDTs) are also in use in such gaging devices.
In many gaging applications, compactness is an essential feature. For example, when measuring a workpiece diameter on an internal grinder, it is desirable to fit the gaging device within the confines of the workhead spindle of the grinder. For example, in some instances related to internal grinding, the measuring device must reach the workpiece diameter through the clearance in the center of the workhead spindle while the grinding wheel enters the workpiece from the opposite side. In such instances, the gage must be sufficiently compact so it makes no contact with the internal diameter of the workhead spindle.
In many gaging operations it is desirable for a gaging device to be readily adaptable for making various ranges of measurement. Typically, a gage device has a pre-determined and fixed measurement range. Only variations within the measurement range provide an output for the gage. In machine operations where various workpieces are machined and various features having varying dimensions must be measured, it is desirable to provide a gaging device useable for such varying situations. At the same time, expanding the measurement range should not occur at the cost of a lack of measurement accuracy.
Designers of gaging devices further strive to achieve temperature stability, accuracy, repeatability, low cost, and low maintenance requirements for the devices.
The caliper gage device in accordance with the present invention, achieves the above-referenced desirable features. The gage device includes a pair of probe tips mounted to a gage body. The gage body is formed from one piece of metal material and is machined, preferably using electrical discharge machining (EDM) processes for forming a number of relatively moving segments. The body features a split along its diametric plane which interacts with an adjustment device to cause these two halves to separate by a desired amount. This separation in turn enables probe tips mounted to the gage body to have varying set positions, without changing the output of the gage device. Thus, the device can be used for making distance measurements over a range of set positions. The design of the gage of the present invention is compact, such that it can be mounted to an internal grinding machine and reach the workpiece through the workhead spindle for diameter measurements. Furthermore, the gage device has few parts which reduce variability and fabrication cost, and improves reliability.